In a control apparatus for driving a servo motor, a feedback loop is generally configured for detecting a rotational velocity or a rotational position of the motor so as to track a velocity command or a position command inputted from outside. In order to ensure operational stability of the feedback loop to sufficiently exert performance for tracking the velocity command or the position command, it is necessary to set appropriate values for a plurality of control parameters included in the feedback loop, namely a velocity gain and a position gain, in accordance with a moment of inertia and a state of the load of the servo motor.
A conventional servo motor control apparatus is mounted with parameter setting means for setting an appropriate value for the foregoing control parameter in accordance with the moment of inertia and the state of the load of the servo motor. Further, techniques with regard to a servo motor control apparatus mounted with such parameter setting means are, for example, disclosed in Patent Documents 1 and 2.
FIG. 29 is a block diagram showing a constitutional example of such a conventional control apparatus for a servo motor (hereinafter simply referred to as “motor” as appropriate).
In FIG. 29, motor 101 is connected with load 102. Motor 101 is also connected with encoder 103, and a value corresponding to a rotational position of motor 101 is outputted. An output value of encoder 103 is subjected to differential processing in differential operation section 111, and velocity detection signal dv indicating a value converted into the rotational velocity of motor 101 is outputted. The velocity command inputted from the outside is inputted into field forward gain multiplying section 110. Simultaneously, this velocity command is used to calculate a difference signal with velocity detection signal dv outputted by differential operation section 111 in subtraction section 114. This signal corresponds to a velocity error, and is inputted into integral operation section 112, to be converted into a signal corresponding to a position error. This signal is inputted into position gain multiplying section 109, multiplied by predetermined position gain Kp, and outputted. Further, the signal outputted from position gain multiplying section 109 is added with a signal of the velocity command outputted after multiplied by predetermined feedforward gain Kf in feedforward gain multiplying section 110, and a signal of a difference from velocity detection signal dv outputted by differential operation section 111 is calculated. Thereafter, the signal outputted from operating section 113 is inputted into velocity gain multiplying section 108, multiplied by predetermined velocity gain Kv and outputted, and based upon this outputted signal, servo motor 101 is driven. It is to be noted that for velocity gain Kv, a value obtained by multiplying a set value of inertia J by a set value of velocity band fv of motor 101 including load 102 in multiplication section 115 is set.
Further, the servo motor control apparatus shown in FIG. 29 is configured as parameter setting means, so as to set set values for inertia J, position gain Kp and velocity band fv included in the control parameters, from the outside.
In such a configuration, foregoing position gain Kp and velocity gain Kv corresponding to velocity band fv are what are referred to as control parameters, and for values of these respective control parameters, values inputted from the outside are set. At this time, these set values have influences on control performance of servo motor 101 and the oscillation stability of feedback loop 104, thereby requiring adjustment of these set values to the optimal values.
Incidentally, in general, the larger the value of velocity band fv, the larger the frequency band width of feedback loop 104, and hence excellent response or tracking can be obtained with respect to an input of the velocity command. On the other hand, load 102 including servo motor 101 generally has mechanical resonance characteristics, and when the value of velocity band fv is made too large, oscillation may occur in feedback loop 104. Further, when the value of position gain Kp is not appropriately given with respect to the value of velocity band fv, a damping factor of feedback loop 104 is affected, resulting in that an appropriate response cannot be obtained with respect to the command from outside due to vibrational response or, on the contrary, deterioration in tracking of the rotational position.
It is therefore necessary to raise or lower values of the respective parameters for adjustment while checking a response of servo motor 101 to the command, and this operation is generally referred to as manual adjustment of control parameters. On the other hand, an adjustment function of automatically adjusting these control parameters, generally referred to as auto tuning, has been in practical use.
However, even when the auto tuning is executed, the control parameters are not necessarily adjusted to optimal values with respect to any state of the load, and hence in the actual situation, the manual adjustment function has also been essential for a typical servo motor control apparatus.
Further, no matter whether manual adjustment or auto tuning is performed, in the case of raising or lowering the respective control parameters for adjustment to the optimal values, oscillation occurs in the feedback loop, leading to strong vibration of the servo motor, which might damage the load of the servo motor. When oscillation occurs in the feedback loop, it is necessary to perform a procedure such as a procedure of changing changed control parameter values again, or a procedure of changing control parameter values after temporarily cutting off and stopping a current flowing in the servo motor, and again flowing the current in the servo motor. There has thus been a problem with such a conventional servo motor control apparatus in that it takes a long time to stop the oscillation, to cause excessive damage on the load of the servo motor, or time and efforts to be expensed for adjustment of the control parameters. A technique with regard to a motor having a function to suppress such mechanical vibration is, for example, disclosed in Patent Document 3.    [Patent Document 1] Unexamined Japanese Patent Publication No. H06-165550    [Patent Document 2] Unexamined Japanese Patent Publication No. H06-319284    [Patent Document 3] Unexamined Japanese Patent Publication No. 2003-52188